Physics Chapter 17 Change of Phase Boiling evaporation

Physics Chapter 17 Change of Phase

• Boiling evaporation beneath the surface since evaporation is a cooling process, boiling must also be a cooling process heating water and boiling water are different depends on temperature depends on pressure lower pressure= decrease boiling point at sea level- boiling point– 100 C in Denver (1 mile above sea level)– 95 C

• Because boiling is a cooling process, you can control the boiling (through pressurization) and use it to freeze items. • Freezing energy is withdrawn until the molecules are moving slowly enough so that the attractive forces between them are able to cause cohesion. at sea level– 0 C can change the freezing point by including an additive like salt or sugar

• Ice to Vapor Add heat to ice- raise the temperature to 0 C for 1 gram of ice, it takes 80 calories to change from ice to water (latent heat of fusion) the temperature of the ice will not change until all the ice has turned to water Add heat to water- raise the temperature to 100 C for 1 gram of water, it takes 540 calories to change from water to vapor (latent heat of vaporization) the temperature of the water will not change until all the water has turned to steam. The water staying 100 C is why boiling is a “cooling process”the water doesn’t get hotter.

Assignment • Click on the link to complete the homework